Update libpng to 1.6.22

third_party/libpng/pnggccrd.c

Index: third_party/libpng/pnggccrd.c
diff --git a/third_party/libpng/pnggccrd.c b/third_party/libpng/pnggccrd.c
deleted file mode 100644
index 2208fb0d79fbd95e5816ef7d6fb85fac0c95c232..0000000000000000000000000000000000000000
--- a/third_party/libpng/pnggccrd.c
+++ /dev/null
@@ -1,26 +0,0 @@
-/* pnggccrd.c
- *
- * Last changed in libpng 1.2.48 [March 8, 2012]
- * Copyright (c) 1998-2002,2004,2006-2012 Glenn Randers-Pehrson
- *
- * This code is released under the libpng license.
- * For conditions of distribution and use, see the disclaimer
- * and license in png.h
- *
- * This code snippet is for use by configure's compilation test. Most of the
- * remainder of the file was removed from libpng-1.2.20, and all of the
- * assembler code was removed from libpng-1.2.48.
- */
-
-#if (!defined _MSC_VER) && \
-    defined(PNG_ASSEMBLER_CODE_SUPPORTED) && \
-    defined(PNG_MMX_CODE_SUPPORTED)
-
-int PNGAPI png_dummy_mmx_support(void);
-
-int PNGAPI png_dummy_mmx_support(void)
-{
-     /* 0: no MMX; 1: MMX supported; 2: not tested */
-     return 2;
-}
-#endif